I. Field of the Invention
This invention relates to rotating cutting tools. In particular, this invention relates to end milling tools, and most particularly to end milling tools providing improved performance for cutting while being advanced simultaneously in the direction of the tool longitudinal axis (infeed), and in a direction transverse to the tool longitudinal (translational feed), such simultaneous feed known as xe2x80x9cramp feedxe2x80x9d.
II. Description of Related Art
End mills are generally cylindrically shaped cutting tools comprising a body portion and shank portion, the body portion including cutting edges and the shank portion typically comprising surfaces for retention by a tool rotating device. Typically, the body portion comprises a tip or end comprising end cutting edges, and a cutting length comprising a plurality of flutes defining side cutting edges terminating at the tip. Known end mills may have straight or helical flutes, and may have two, three, four or more flutes and two, three, four, or more end cutting edges. It is known to arrange end cutting edges to lie along radii at the tip and to provide channels or gashes in the tip inter-spaced with end cutting edges and continuous between the tip circumference and the interior of the tip proximate the tip center. Further, it is known to have end cutting edges lie in planes oblique to the tool longitude and sloping at relatively shallow angles from the tool periphery toward the tip center.
U.S. Pat. No. 2,129,417 discloses an end mill having an arcuate depression in the tip end interiorly of the end cutting edges such that the end cutting edges are of relatively short effective length and are well supported by the sloping sides of the arcuate depression. The end mill disclosed is described as having improved resistance to chipping of the end cutting edges.
U.S. Pat. No. 5,049,009 discloses an end mill wherein end cutting edge portions, lying parallel to radii at the tip, slope shallowly inwardly from the tip periphery toward the shank end and intersect at the tip center. A primary land (referred to as a xe2x80x9cfirst back-off surfacexe2x80x9d) lies between each end cutting edge portion and a relief surface intersecting trailing side non-cutting surfaces.
U.S. Pat. No. 5,779,399 discloses an end mill wherein only one end cutting edge lies along a radius at the tip and extends from the periphery through the tip center. As shown in this reference, relief is provided in the tip end behind the end cutting edge and between the end cutting edge and a sidewall of a gash. The end cutting edge of this reference lies in a plane perpendicular to the tool longitude.
Known end mills tend to chatter during ramp feeding at nominal feed rates because of the relatively high forces acting on the trailing side of the tip end. To avoid tool chatter, it is conventional to reduce feed rates below nominal values during ramp feeding. Consequently, there is a need for an end mill providing improved cutting performance during ramp feeding, particularly exhibiting reduced chatter inducing forces and allowing feed at nominal feed rates.
It is an object of the present invention to provide an end mill exhibiting free cutting in ramp feeding whereby forces are reduced.
It is a further object of the present invention to provide an end mill providing improved delivery of coolant to the end cutting edge.
Further objects and advantages of the invention shall be made apparent from the accompanying drawings and the following description thereof.
In accordance with the aforesaid objects, the present invention provides an end mill wherein end cutting edges parallel radii of the tip and lie along primary and secondary slopes from the tool periphery inwardly. The primary slope is relatively shallow and over a relatively short portion of the cutting edge, the secondary slope is relatively steep and extends over the greater portion of the end cutting edge. The tip includes a land adjacent each end cutting edge and the primary slope provides relief in this land behind the peripheral edge of the land. The secondary slope promotes delivery of coolant proximate the primary slope and evacuation of chips from the cutting zone.